Syria: UN aid chief calls for urgent ceasefire in Muadhamiya
The UN's humanitarian chief has called for an "immediate pause in hostilities" in Muadhamiya, a rebel-held suburb of the Syrian capital, Damascus.
Valerie Amos said 3,000 people were evacuated last Sunday, but that the same number were trapped in the town amid continuing shelling and fighting.
Thousands of people were in a similar situations in towns across the country, she said.
The army has previously said rebel-held areas must surrender or starve.
Also on Saturday, activists said at least 16 soldiers were killed in a suicide bombing and fighting at a checkpoint near the mainly-Christian area of Jaramana.
State media blamed "terrorists" for the explosion but did not give details.
Rebels control much of the countryside around Damascus but Jaramana - a Christian and Druze area mostly loyal to President Bashar al-Assad - is still held by the government.
In a statement, Baroness Amos said was "extremely worried by the situation unfolding across Syria where ordinary women, children and men are facing horrific violence and brutality from all sides of the conflict".
She said relief workers had been unable to access Muadhamiya for months, and that the ongoing conflict was preventing any rescue mission from going ahead.
"I call on all parties to agree an immediate pause in hostilities in Muadhamiya to allow humanitarian agencies unhindered access to evacuate the remaining civilians and deliver life-saving treatment and supplies in areas where fighting and shelling is ongoing," she said.
But she said this was not the only area of concern, citing Nubil, Zahra, old Aleppo town, old Homs town and Hassaka as other places where people were in danger.
"Civilians must be allowed to move to safer areas without the fear of attack," she added.
"It is vital that all parties to the conflict respect their obligations under international human rights and humanitarian laws to protect civilians and to allow neutral, impartial humanitarian organizations safe access to all people in need, wherever they are in Syria."
Muadhamiya and at least two other Damascus's suburbs - Yarmouk and Eastern Ghouta - have been besieged by government forces for several months.
The situation has become so desperate that earlier this week Muslim clerics issued a religious ruling allowing people to eat cats, dogs and donkeys just to survive.
Those animals are usually considered unfit for human consumption in Islam.
Syrian activists say they are now starting to record the first deaths of complications caused by malnutrition.
On Friday, the US urged the Syrian government to allow relief convoys to reach starving civilians.
State Department spokeswoman Jen Psaki warned that "those who are responsible for atrocities in the Damascus suburbs and across Syria must be identified and held accountable".
More than 100,000 people have been killed in Syria's conflict, now in its third year. The unrest began in the midst of the Arab Spring regional uprisings, with protests against President Bashar Assad, before degenerating into civil war.
A British surgeon who volunteered in a hospital in northern Syria for five weeks told the BBC on Friday that he had treated pregnant women deliberately targeted by snipers.
David Nott said there "was definitely a game going on between the snipers".
"One day we would receive patients who had purely groin wounds, another day purely chest wounds or purely abdominal wounds. Then another day full-term pregnant ladies were coming in having been shot."
Most of the unborn babies and many of the women did not survive, he said.
International efforts to halt the violence have consistently faltered, but last month the UN Security Council broke its deadlock, voting unanimously to adopt a binding resolution on ridding the country of chemical weapons.
The move followed international outrage at a chemical weapons attack near Damascus in August.
UN experts are currently working in Syria, inspecting chemical weapons sites and destroying the arsenal, and say they have completed almost half their mission.